Skip Navigation

Cardiovascular Research 1998 39(1):148-154; doi:10.1016/S0008-6363(98)00107-2
© 1998 by European Society of Cardiology
This Article
Right arrow Extract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow E-letters: Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when E-letters are posted
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Shah, A. M
Right arrow Articles by Lakatta, E. G
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Shah, A. M
Right arrow Articles by Lakatta, E. G
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

Copyright © 1998, European Society of Cardiology

Physio-pharmacological evaluation of myocardial performance: an integrative approach

Ajay M Shaha,*, Steven J Sollottb and Edward G Lakattab

aDepartment of Cardiology, University of Wales College of Medicine, Heath Park, Cardiff, CF4 FXN, UK
bLaboratory of Cardiovascular Science, Gerontology Research Center, NIA, National Institutes of Health, Baltimore, USA

* Corresponding author. Tel.: +44 1222 742338; Fax: +44 1222 743500; E-mail: shaham2@cf.ac.uk

Received 16 March 1998; accepted 17 March 1998

KEYWORDS Contractive function; Endothelial function; Myocytes; Ventricular function

Despite major advances in the understanding of cardiovascular physiology and pathophysiology and the development of new therapies in the 20th century, cardiovascular disease is projected to become the leading overall cause of mortality worldwide within the next couple of decades [1]. In the western world, an increasing proportion of older people in the population accounts for the lack of reduction in the absolute number of cardiovascular deaths, whereas in developing countries, part of the reason is the adoption of "western" lifestyles and their accompanying coronary risk factors as socioeconomic status gradually improves and mortality from infectious and other diseases of early life decrease. There remain significant gaps in our understanding of many aspects of cardiovascular diseases and the contribution of risk factors such as smoking, hypercholesterolaemia, hypertension and diabetes. In addition, increasing numbers of patients who survive ischaemic cardiac disorders develop heart failure.

Traditionally, the focus of research into cardiovascular disease was the heart and myocardium, but in the last several decades, the importance of the vasculature and of other body systems has been better appreciated. The field of vascular biology has blossomed. Traditionally, investigators focused on mechanical function. However, in the last several decades, investigative approaches have broadened dramatically, ranging from molecular and cellular biology and physiology, to in vitro and in vivo studies in animal models of disease, to studies of individual human subjects, to population genetics and epidemiology. The methodologies available and their precision have altered out of all recognition compared to the approaches of 40–50 years ago.

Within this context, the questions that are considered in this article are: How should myocardial performance best be assessed? What are the advantages and disadvantages of currently used methodologies? How far can and should reductionism be pursued? What is the relevance of animal models? The implicit pre-requisite in answering these questions is that information obtained using any particular approach should, ultimately, be of some relevance to human cardiovascular function or dysfunction.

Although we focus in this counterpoint article on the in vitro assessment of myocardial contractile behaviour, it is clear that many other aspects of cardiac function as well as that of other organs will be relevant to the understanding of cardiovascular disorders. Within the heart, coronary vascular function, endothelial function, the influence of blood cells, neural control, the release of circulating hormones, such as natriuretic peptides, locally active paracrine and autocrine substances, and the properties of the extracellular matrix may all be relevant to contractile function as well as other aspects, such as energetics, growth, hypertrophy and so on. With respect to the contractile process itself, and its regulation, a full understanding requires information about excitation–contraction coupling, signal transduction, myofilament mechanisms, energetics and molecular mechanisms, to name but a few relevant aspects.

Given this complexity, it is naive to imagine that any single model system could provide all of the necessary information. Logically, appropriate integration of information, acquired using multiple complementary modern approaches in tandem, is more likely to clarify the complexity of the intact system. In other words, the science of "integrative physiology". Advantage may then be taken of the huge technical and conceptual advances in, for example, molecular and cellular biology in recent decades. The integration of such data into the "big picture" is not synonymous with simple multiplication or addition, given the non-linearity of most biological systems. Inevitably, each successive reduction in scale of the model system results in the loss of some variables that normally influence function in the intact organ, while allowing more precise assessment of the remaining variables. In putting together the pieces of information derived from such an approach, the critical requirements for the cardiovascular researcher are an awareness of (a) the advantages and limitations of individual methodologies, (b) the limits of extrapolation to other model systems, (c) the necessity to confirm and validate data or hypotheses generated in one model system in other systems (and ultimately in humans).

We now consider critically some of the approaches that are in current use for the investigation of cardiac contractile properties in vitro. Clearly, it is not possible within the confines of this article to be comprehensive either with respect to methodology or to work cited, and we have accordingly been selective.


   1 The isolated heart
Top
 1 The isolated heart
2 Isolated papillary muscle...
 3 Isolated cardiac myocytes
 4 Subcellular model systems
 5 The use of...
 6 Conclusions
 References
 
This is the only isolated preparation that allows measurement of global cardiac function, generally either isovolumic or ejecting. In the case of the ejecting heart, careful control of ventricular pre-load, afterload and heart rate, and assessment of pump function is feasible. Another important advantage over other isolated preparations is the fact that the coronary circulation is maintained intact. The inter-relationship between coronary vascular and ventricular properties may therefore be explored. With respect to the influence of the endothelium on myocardial function, this is the only isolated preparation in which endothelial cells in situ (i.e., not isolated cells) are subject to physiologically relevant stimuli, such as flow-induced shear and mechanical forces (especially in the ejecting heart) [2–6]. It is important in this context to bear in mind that the endothelium exerts a remarkably subtle and complex influence on vascular and myocardial function. For instance, there will be complex interactions among many endothelium-derived mediators with respect both to their release and their myocardial actions [7, 8]. A thorough evaluation of these interactions will require a broad range of complementary experimental approaches.

A significant limitation of crystalloid-perfused isolated hearts, especially Langendorff preparations, is their abnormally high basal coronary flow, altered flow regulation and increased tissue water content [9, 10]. These problems may, to a large extent, be circumvented by the use of blood-perfused organs [11, 12]. Also, in the Langendorff heart, the use of intraventricular balloons could damage the endocardial endothelium and potentially influence global function, although these effects are likely to be of small magnitude. The combination of measurements of pump function with the assessment of other parameters, such as energetics (by magnetic resonance spectroscopy) [13, 14], cytosolic Ca2+ (e.g., by fluorescence spectrometry or aequorin luminescence) [15, 16], monophasic action potentials [15], labile radical species (by electron paramagnetic resonance and chemiluminescence) [17], and other biochemical indices, has substantially improved the utility of these preparations.


   2 Isolated papillary muscle and trabecular preparations
Top
 1 The isolated heart
 2 Isolated papillary muscle...
3 Isolated cardiac myocytes
 4 Subcellular model systems
 5 The use of...
 6 Conclusions
 References
 
A more precise assessment of the mechanical properties of muscle has been greatly facilitated in the isolated papillary muscle or trabecular preparation, where it is possible to accurately measure (and control) force and length in a multicellular preparation with relatively simple geometry. Indeed, many fundamental aspects of current concepts of muscle mechanics have been based on studies in this preparation, dating back nearly 40 years [18–20].

Before the advent of techniques that allowed direct measurement, there were also widespread attempts to deduce mechanisms of excitation–contraction coupling and the crossbridge cycle itself from the macroscopic behaviour of whole muscle (e.g., based on mechanical correlates, such as force–time relations, rate of force development and unloaded shortening velocity). However, it became clear as early as the 1970s that there were serious limitations with this approach. The papillary muscle preparation has a high series elasticity because of end compliance, related to damaged muscle ends and the compliance of attached recording devices. This results, in many cases, in significant (up to 12% Lmax or more) mid-segmental shortening during "isometric" contractions [21–24]. The resultant spatial inhomogeneity (e.g., of sarcomere length and intracellular Ca2+) may invalidate many of the assumptions required for the above deductive approach. Likewise, measurements of "maximal" unloaded shortening velocity are likely to be substantially affected by small internal loads that are impossible to avoid in non-isosarcometric preparations [20]. Furthermore, there is no simple relationship between active and passive elements in this preparation [24].

Other problems of the superfused papillary muscle preparation relate to adequacy of oxygenation and substrate supply, the build-up of metabolites, such as inorganic phosphate, and concentration gradients [25]. Appropriate selection of preparations for study, based for example on very low cross-sectional areas, is therefore critical. With regard to the influence of endothelial cells on myocardial function, it is important to note that the most relevant cell type in the whole heart, the coronary vascular endothelial cell, is probably non-functional in this preparation (unless it is perfused). Although the interaction between endocardial endothelial cells and subjacent myocytes may be quite well studied in the papillary muscle [7, 8, 26], there are significant functional differences between endocardial and coronary vascular endothelial cells [26]. In addition, important and relevant aspects of endothelial function, such as cyclical mechanotransduction (e.g., mediated by shear stress) are, to a large extent, inoperative. The subtleties of endothelial and myocardial subcellular signalling processes, the release of paracrine mediators and interactions among these substances are difficult to accurately assess in this preparation. Thus, complementary approaches, such as the use of model systems that allow clear separation between different cell types (i.e., pure endothelial cells and pure cardiac myocytes) [7, 27], and those in which vascular endothelial cells in situ are subject to physiologically relevant mechanical stimuli (i.e., isolated heart preparations) [4–8], are required.

In view of the limitations discussed above, although the papillary muscle remains a useful and relatively simple preparation for the purposes of measuring contractile function, the assessment of contractile mechanisms is fraught with difficulty. However, a number of recent technical advances have the potential to overcome some of these problems. Among the most important of these is the ability to obtain true isosarcometric contractions, using laser diffraction to monitor sarcomere length and adaptive control systems to regulate it [28–30]. Interestingly, this approach suggests that deductions based on studies using "isometric" conditions may be incorrect. For example, the main determinant of isosarcometric twitch prolongation appears to be the peak twitch force (which is influenced by cytosolic Ca2+ as well as myofilament responsiveness to Ca2+), whereas sarcomere length itself has no independent effect, contrary to speculations based on studies in "isometric" muscle [29]. The incorporation of objective measurement of variables such as intracellular Ca2+ transients, ATPase activity, heat production and O2 consumption (e.g., [29–34]) is a major advance over much less precise and speculative interpretative assessments based solely on mechanical correlates. Other advances include the use of skinned fibres with careful, uniform control of Ca2+ levels for studying Ca2+–myofilament interaction, and the use of caged compounds (e.g., [35, 36]). However, an unresolved and major limitation of the papillary muscle preparation is the fact that it is not possible to undertake voltage clamp studies, thus greatly diminishing its usefulness in studying excitation–contraction coupling processes.


   3 Isolated cardiac myocytes
Top
 1 The isolated heart
 2 Isolated papillary muscle...
 3 Isolated cardiac myocytes
4 Subcellular model systems
 5 The use of...
 6 Conclusions
 References
 
The advent of the isolated Ca2+-tolerant cardiac myocyte preparation opened up the possibility of addressing the fundamental mechanisms of excitation–contraction coupling and contraction that underlie myocardial function, in a preparation devoid of the complicating effects of other cell types or of extracellular structures. It has also enabled the careful assessment of cell-specific phenomena (e.g., cellular biochemical processes, gap junctional communication using cell tandems, gene and protein expression, etc.) that may be difficult or even impossible to dissect in multicellular systems. Further refinements include myocyte culture (enabling, for example, the study of growth and differentiation, and genetic manipulation), the use of embryonic stem cell systems, the assessment of cell–cell interactions with pure endothelial or neuronal (and other) cells, and so on. We focus here on contractile function and its underlying mechanisms.

In most studies, the measurement of contractile function in this preparation has been confined to the shortening of externally unloaded cells (measured optically), although technically more difficult procedures, such as the measurement of force production, external loading and control of sarcomere length, have been undertaken by several workers [37–42]. It was important early on to demonstrate that isolated single cardiac myocytes of several species retained the Ca2+-dependent systolic and diastolic properties of intact muscle, e.g., with respect to their resting membrane potential and excitability, spontaneous Ca2+ release from the sarcoplasmic reticulum and the effects of changes in stimulation frequency or extracellular Ca2+ concentration [43]. It was also shown that modelling based on measurement of isolated single cell properties and behaviour appropriately predicted the bulk properties of intact muscle, e.g., with respect to maximum inotropy achieved with a variety of Ca2+-elevating interventions [44]. Numerous studies have now demonstrated that myocyte shortening responses to a wide variety of interventions parallel those of force or shortening changes in intact tissue, e.g., the responses to {alpha}- and β-adrenergic agonists, endothelin, Ca2+ sensitisers and desensitisers, opioid peptides, modulation of sarcoplasmic reticular function (with caffeine, ryanodine or thapsigargin), acidosis, alkalosis, hypoxia–reoxygenation, electrical tetanisation and stimulation of the nitric oxide/cGMP pathway (e.g., [24, 43–56]). This parallel pattern of response between myocytes and intact multicellular muscle is consistent with the findings that, over a wide range of cell (or sarcomere) lengths, changes in cell length are linearly related to changes in force [57]. Similarly, force and shortening responses to widely varying interventions have been shown to parallel each other in human papillary muscle [58].

The utility of the single myocyte preparation has been enormously enhanced by advances that have enabled concomitant measurement with high spatial and temporal resolution of variables such as membrane currents (with voltage clamp techniques) and intracellular ion (Ca2+, H+, Na+) concentrations (with fluorescence spectrometry, imaging and confocal microscopy) (e.g., [40–42, 46, 48–52, 59–61], and reviewed in refs. [62–64]). Indeed, much of our current understanding of the mechanisms of excitation–contraction coupling is based largely on studies in single cells [59–64]. Likewise, major advances in understanding Ca2+ oscillations and cellular mechanisms of dysrrhythmia have come from studies in single cells. Simultaneous measurements of cytosolic Ca2+ and cell shortening have also provided significant information regarding the inter-relationship between these variables, especially with respect to a variety of inotropic interventions. Techniques have been developed to enable measurement of the "steady-state" relationship between these variables during tetanisation of intact cells, as an approach to the assessment of myofilament response to Ca2+ in intact cells with intact signalling pathways [27, 48, 50, 52]. Such techniques can provide useful data that is complementary to the detailed analyses of Ca2+–myofilament interaction possible in skinned tissue, since, in the latter preparation, membrane receptors and signalling pathways will usually be inoperative.

Although myocyte shortening responses, in general, parallel inotropic responses of intact tissue, pertinent questions that require critical attention are (a) to what extent are there differences in response between the two situations and (b) what are the limitations of the myocyte preparation? In most studies, the isolated cardiac myocyte is not subjected to any significant external mechanical load. Thus, load-dependent effects on contractile properties, e.g., changes in relaxation pattern [65], cannot usually be addressed. Secondly, although the isolated myocyte has a remarkable degree of regional sarcomere uniformity (both at rest and during isotonic contraction) [66], sarcomere length is not usually controlled. Thus, length-dependent effects on contractile function are also not usually possible to address. Thirdly, the contribution of "passive" cellular elasticity and restoring forces to the shortening responses of myocytes requires careful attention. Since the externally unloaded myocyte will usually shorten below slack length, the contribution of "passive" cellular elasticity may be most relevant in terms of resistance to shortening and in generating restoring forces, whereas in isometric preparations (whether single or multi-cellular), resistance to stretch is of greater relevance [24]. In either case (i.e., resistance to shortening or to stretch), the myofibrillar protein titin is thought to have a major role in healthy myocardium, acting as a bidirectional spring [67–69]. Cytoskeletal components, such as microtubules, may also be important in neonatal myocardium [24, 70], especially with respect to myofibrillogenesis, but are not thought to play a significant role in the contractile function of healthy adult myocardium [24, 71]. In pressure-overload hypertrophy, however, an excess of cytoskeletal tubulin is thought to interfere with contractile function by imposing a viscous intracellular load on the shortening sarcomere and by increasing passive stiffness [71, 72]. It is important to note, therefore, that "passive" cellular elasticity is relevant in all intact myocardial preparations (single or multi-cellular), but that the precise influence on contractile function varies between these preparations. The effect of restoring forces in the isolated myocyte may be more in restoring diastolic cell length than in influencing the length–tension relation [24], since the measured restoring force in relaxing myocytes has been estimated to be only of the order of ~4% of the total active force [73, 74]. In fact, the quiescent unloaded myocyte may be uniquely sensitive in indexing small alterations in "passive" properties, which are reflected in Ca2+-independent changes in optically measured resting cell length [48, 52]or, more directly, in changes in stiffness [72]. While this cellular component of "passive" elasticity may not necessarily make a very large contribution to overall elasticity in most physiological circumstances, it could be a significant factor in pathological situations (e.g., pressure-overload hypertrophy [71, 72]and diastolic heart failure [7]). Accurate detection of such changes in intact cardiac myocytes in recent studies has indicated the capacity of agents such as the calcium desensitiser, butanedione monoxime (BDM) [48], the calcium sensitiser, EMD 53998 [48], 8-bromo-cGMP [52], endothelial cell-derived substances [27]and microtubule depolymerising agents (in hypertrophied myocardium) [72]to acutely alter "passive" cell properties. By contrast, in intact healthy multicellular preparations, although cellular factors contribute substantially to overall "passive" elasticity, particularly at lower sarcomere lengths [24], accurate measurement of changes in these properties is problematic because of the complicating effects of extracellular factors (e.g., collagen) and the (relatively) lower resolution and signal-to-noise ratio of force measurements.


   4 Subcellular model systems
Top
 1 The isolated heart
 2 Isolated papillary muscle...
 3 Isolated cardiac myocytes
 4 Subcellular model systems
5 The use of...
 6 Conclusions
 References
 
Questions regarding the limits of reductionism perhaps pertain most to approaches that involve the use of subcellular model systems or non-"intact" tissue. Is it valid to argue that such experimental models should not be used in the investigation of contractile properties or in the investigation of specific topics, such as the interactions between endothelial cells, cytokines and cardiac myocytes [75]. On the contrary, in our view, such strategies, in tandem with other approaches, have a great deal to offer. Taking the example of the influence of endothelial cell factors and cytokines on myocardial function, the understanding of the subcellular mechanisms of mediators such as nitric oxide and endothelin is clearly relevant. Studying the effects on signal transduction, excitation–contraction coupling processes, myofilament properties, mitochondrial function and molecular mechanisms will undoubtedly be (and has been) informative (e.g., [27, 53, 56, 76–82]). The important requirements, as stated previously, are clarity about the specific questions being addressed, the limitations of individual methodologies, the limits of extrapolation to other model systems and the necessity to confirm or validate data using independent experimental approaches.


   5 The use of animal models
Top
 1 The isolated heart
 2 Isolated papillary muscle...
 3 Isolated cardiac myocytes
 4 Subcellular model systems
 5 The use of...
6 Conclusions
 References
 
Most of the experimental approaches discussed above have been employed predominantly in animal tissues. The relevance or otherwise of data so obtained to human cardiac function and dysfunction is a pertinent issue. Differences between species have (rightly) been emphasised for as long as animal tissues have been experimentally studied. However, recent advances in molecular genetics and cell biology demonstrate the remarkably high degree of conservation of cellular protein structure and function across a broad range of mammalian (and non-mammalian) species [83–85]. The development of animal models of human disease, using various pharmacological, breeding and operative procedures, as well as transgenic and knockout technology, has also demonstrated their close similarity to human pathophysiology [83, 84]. As with the use of various in vitro procedures, these animal models have proven and will continue to be extremely useful, although the limitations of individual models have to be recognised.


   6 Conclusions
Top
 1 The isolated heart
 2 Isolated papillary muscle...
 3 Isolated cardiac myocytes
 4 Subcellular model systems
 5 The use of...
 6 Conclusions
References
 
Adequate evaluation and understanding of cardiac performance is not limited simply to the study of heart muscle, nor indeed to contractile function, or even just to the mechanical properties of myocardial tissue alone. With respect to the investigation of contractile function, data regarding aspects such as excitation–contraction coupling, signal transduction, myofilament mechanisms, energetics and molecular mechanisms, as well as pure muscle mechanics, will all be relevant. No single experimental approach is uniquely suited to the physio-pharmacological evaluation of myocardial performance. Different experimental approaches each have their advantages and limitations. Appropriate integration of data derived from multiple complementary methodologies is the best approach, and one that will benefit from the major technical and conceptual advances of recent decades.

Time for primary review 14 days.


   Acknowledgements
 
AMS is supported by the UK Medical Research Council and the British Heart Foundation. SJS and EGL are supported by the NIH–NIA Intramural Research Program.


   References
Top
 1 The isolated heart
 2 Isolated papillary muscle...
 3 Isolated cardiac myocytes
 4 Subcellular model systems
 5 The use of...
 6 Conclusions
 References
 

  1. Braunwald E. Shattuck lecture — Cardiovascular medicine at the turn of the millennium: Triumphs, concerns, and opportunities. New Engl J Med (1997) 337:1360–1369.[Free Full Text]
  2. Lamontagne D, Pohl U, Busse R. Mechanical deformation of vessel wall and shear stress determine the basal release of endothelium-derived relaxing factor in the intact rabbit coronary vascular bed. Circ Res. (1992) 70:123–130.[Abstract/Free Full Text]
  3. Ueeda M, Silvia S.K, Olsson R.A. Nitric oxide modulates coronary autoregulation in the guinea pig. Circ Res (1992) 70:1296–1303.[Abstract/Free Full Text]
  4. Grocott-Mason R.M, Anning P.B, Evans H, et al. Modulation of left ventricular relaxation in isolated ejecting heart by endogenous nitric oxide. Am J Physiol (1994) 267:H1804–H1813.[Web of Science][Medline]
  5. Pinsky D.J, Patton S, Mesaros S, et al. Mechanical transduction of nitric oxide synthesis in the beating heart. Circ Res (1997) 81:372–379.[Abstract/Free Full Text]
  6. Prendergast B.D, Sagach V, Shah A.M. Basal release of nitric oxide augments the Frank-Starling response in the isolated heart. Circulation (1997) 96:1320–1329.[Abstract/Free Full Text]
  7. Shah A.M. Paracrine modulation of heart cell function by endothelial cells. Cardiovasc Res (1996) 31:847–867.[Abstract/Free Full Text]
  8. Winegrad S. Endothelial cell regulation of contractility of the heart. Annu Rev Physiol (1997) 59:505–525.[CrossRef][Web of Science][Medline]
  9. Fiegl E.O, Neat G.W, Huang A.H. Interrelationships between coronary artery pressure, myocardial metabolism and coronary blood flow. J Mol Cell Cardiol (1989) 22:375–390.[Web of Science]
  10. Rubboli A, Sobotka P.A, Euler D.E. Effect of acute edema on left ventricular function and coronary vascular resistance in the isolated rat heart. Am J Physiol (1994) 267:H1054–H1061.[Web of Science][Medline]
  11. Goto Y, Slinker B.K, LeWinter M.M. Effect of coronary hyperemia on Emax and oxygen consumption in blood-perfused rabbit hearts. Energetic consequences of Gregg's phenomenon. Circ Res (1991) 68:482–492.[Abstract/Free Full Text]
  12. Saeki A, Recchia F.A, Senzaki H, Kass D.A. Minimal role of nitric oxide in basal coronary flow regulation and cardiac energetics of blood-perfused isolated canine heart. J Physiol (1996) 491:455–463.[Abstract/Free Full Text]
  13. Gadian D.G, Radda G.K. NMR studies of tissue metabolism. Ann Rev Biochem (1981) 50:69–84.[CrossRef][Web of Science][Medline]
  14. Gross W.L, Bak M.I, Ingwall J.S, et al. Nitric oxide regulates rat heart contractile reserve and inhibits creatinine kinase. Proc Natl Acad Sci USA (1996) 93:5604–5609.[Abstract/Free Full Text]
  15. Lee H.C, Mohabir R, Smith N, Franz M.R, Clusin W.T. Effect of ischemia on calcium-dependent fluorescence transients in rabbit hearts containing indo 1. Correlation with monophasic action potentials and contraction. Circulation (1988) 78:1947–1959.
  16. Kihara Y, Grossman W, Morgan J.P. Direct measurements of changes in intracellular calcium transients during hypoxia, ischemia, and reperfusion of the intact mammalian heart. Circ Res (1989) 65:1029–1044.[Abstract/Free Full Text]
  17. Wang P.H, Zweier J.L. Measurement of nitric oxide and peroxynitrite generation in the postischemic heart — evidence for peroxynitrite-mediated reperfusion injury. J Biol Chem (1996) 271:29223–29230.[Abstract/Free Full Text]
  18. Abbott B.C, Mommaerts W.F.H.M. A study of inotropic mechanisms in the papillary muscle preparation. J Gen Physiol (1959) 42:533–551.[Abstract/Free Full Text]
  19. Brutsaert D.L, Sonnenblick E.H. Force–velocity–length–time relations of the contractile elements in heart muscle of the cat. Circ Res (1969) 24:137–149.[Abstract/Free Full Text]
  20. Ford L.E. Mechanical manifestations of activation in cardiac muscle. Circ Res (1991) 68:621–637.[Free Full Text]
  21. Krueger J.W, Pollack G.H. Myocardial sarcomere dynamics during isometric contraction. J Physiol (1975) 251:627–643.[Abstract/Free Full Text]
  22. Huntsman L.L, Day S.R, Stewart D.K. Nonuniform contraction in the isolated cat papillary muscle. Am J Physiol (1977) 233:H613–H616.[Web of Science][Medline]
  23. Pinto J.G, Win R. Non-uniform strain distribution in papillary muscles. Am J Physiol (1977) 233:H410–H416.[Web of Science][Medline]
  24. Brady A.J. Mechanical properties of isolated cardiac myocytes. Physiol Rev (1991) 71:413–428.[Abstract/Free Full Text]
  25. Kentish J.C, Jewell B.R. Some characteristics of Ca2+-regulated force production in EGTA-treated muscles from rat heart. J Gen Physiol (1984) 84:83–99.[Abstract/Free Full Text]
  26. Brutsaert D.L, Andries L.J. The endocardial endothelium. Am J Physiol (1992) 263:H985–H1002.[Web of Science][Medline]
  27. Shah A.M, Mebazaa A, Yang Z.K, et al. Inhibition of myocardial crossbridge cycling by hypoxic endothelial cells. A potential mechanism for matching oxygen supply and demand? Circ Res (1997) 80:688–698.[Abstract/Free Full Text]
  28. Ter Keurs H.E.D.J, Rijnsburger W.H, Van Heuningen R, Nagelsmit M.J. Tension development and sarcomere length in rat cardiac trabeculae: evidence of length-dependent activation. Circ Res (1980) 46:703–714.[Free Full Text]
  29. Janssen P.M.L, Hunter W.C. Force, not sarcomere length, correlates with prolongation of isosarcometric contraction. Am J Physiol (1995) 269:H676–H685.[Web of Science][Medline]
  30. Janssen P.M.L, de Tombe P.P. Uncontrolled sarcomere length shortening increases the intracellular Ca2+ transient in rat cardiac trabeculae. Am J Physiol (1997) 272:H1892–H1897.[Web of Science][Medline]
  31. Yue D.T, Marban E, Wier W.G. Relationship between force and intracellular [Ca2+] in tetanized mammalian heart muscle. J Gen Physiol (1986) 87:223–242.[Abstract/Free Full Text]
  32. Backx P.H, Gao W.-D, Azan-Backx M.D, Marban E. The relationship between contractile force and intracellular [Ca2+] in intact rat cardiac trabeculae. J Gen Physiol (1995) 105:1–19.[Abstract/Free Full Text]
  33. Hasenfuss G, Mulieri L.A, Allen P.D, Just H, Alpert N.R. Influence of isoproterenol and ouabain on excitation–contraction coupling, cross-bridge function, and energetics in failing human myocardium. Circulation (1996) 94:3155–3160.[Abstract/Free Full Text]
  34. Guth K, Wojciechowski R. Perfusion cuvette for the simultaneous measurement of mechanical, optical and energetic parameters of skinned muscle fibers. Pflug Arch Eur J Physiol (1984) 407:552–557.[CrossRef]
  35. Solaro R.C, Wise R.M, Shiner J.S, Briggs F.N. Calcium requirements for cardiac myofibrillar activation. Circ Res (1974) 34:525–530.[Abstract/Free Full Text]
  36. Homsher E, Millar N.C. Caged compounds and striated muscle contraction. Annu Rev Physiol (1990) 52:875–896.[CrossRef][Web of Science][Medline]
  37. Shepherd N, Kavaler F. Direct control of contraction force of single frog atrial cells by extracellular ions. Am J Physiol (1986) 251:C653–C661.[Web of Science][Medline]
  38. Tarr M. Mechanical and contractile properties of isolated single intact cardiac cells. Adv Exp Med Biol (1988) 161:199–216.
  39. Kent R.L, Mann D.L, Urabe Y, et al. Contractile function of isolated feline cardiocytes in response to viscous loading. Am J Physiol (1989) 257:H1717–H1727.[Web of Science][Medline]
  40. Shepherd N, Vornanen M, Isenberg G. Force measurements from voltage-clamped guinea pig ventricular cells. Am J Physiol (1990) 258:H452–H459.[Web of Science][Medline]
  41. White E, Le Guennec J.Y, Nigretto J.M, et al. The effects of increasing length on auxotonic contractions: membrane potential and intracellular calcium transients in single guinea-pig ventricular myocytes. Exp Physiol (1993) 78:65–78.[Abstract]
  42. Sollott S.J, Lakatta E.G. Novel method to alter length and load in isolated mammalian cardiac myocytes. Am J Physiol (1994) 267:H1619–H1629.[Web of Science][Medline]
  43. Capogrossi M.C, Kort A.A, Spurgeon H.A, Lakatta E.G. Single adult rabbit and rat cardiac myocytes retain the Ca2+- and species-dependent systolic and diastolic contractile properties of intact muscle. J Gen Physiol (1986) 88:589–613.[Abstract/Free Full Text]
  44. Capogrossi M.C, Stern M.D, Spurgeon H.A, Lakatta E.G. Spontaneous Ca2+ release from the sarcoplasmic reticulum limits Ca2+-dependent twitch potentiation in individual cardiac myocytes. A mechanism for maximum inotropy in the myocardium. J Gen Physiol (1988) 91:133–155.[Abstract/Free Full Text]
  45. Harding S.E, Vescovo G, Kirby M, et al. Contractile responses of isolated adult rat and rabbit cardiac myocytes to isoproterenol and calcium. J Mol Cell Cardiol (1988) 20:635–647.[CrossRef][Web of Science][Medline]
  46. Gambassi G, Spurgeon H.A, Lakatta E.G, Blank P.S, Capogrossi M.C. Different effects of {alpha}- and β-adrenergic stimulation on cytosolic pH and myofilament responsiveness to Ca2+ in cardiac myocytes. Circ Res (1992) 71:870–882.[Abstract/Free Full Text]
  47. Kelly R.A, Eid H, Kramer B.K, et al. Endothelin enhances the contractile responsiveness of adult rat ventricular myocytes to calcium by a pertussis toxin-sensitive pathway. J Clin Invest (1990) 86:1164–1171.[Web of Science][Medline]
  48. Lakatta EG, Sollott SJ, Janczewski AM, et al. Mechanisms of relaxation: perspectives from studies in single cardiac cells. In: Lorell BH, Grossman W, editors. Diastolic relaxation of the heart, Boston, MA: Kluwer Academic Publishers, 1994, 149–165.
  49. Ventura C, Capogrossi M.C, Spurgeon H.A, Lakatta E.G. {kappa}-Opioid peptide receptor stimulation increases cytosolic pH and myofilament responsiveness to Ca2+ in cardiac myocytes. Am J Physiol (1991) 261:H1671–H1674.[Web of Science][Medline]
  50. Spurgeon H.A, du Bell W.H, Stern M.D, et al. Cytosolic calcium and myofilaments in single rat cardiac myocytes achieve a dynamic equilibrium during twitch relaxation. J Physiol (1992) 447:83–102.[Abstract/Free Full Text]
  51. Piper H.M, Noll T, Siegmund B. Masterclass: Mitochondrial function in the oxygen depleted and reoxygenated myocardial cell. Cardiovasc Res (1994) 28:1–15.[Free Full Text]
  52. Shah A.M, Spurgeon H, Sollott S.J, Talo A, Lakatta E.G. 8-Bromo-cyclic GMP reduces the myofilament response to calcium in intact cardiac myocytes. Circ Res (1994) 74:970–978.[Abstract/Free Full Text]
  53. Balligand J.L, Kobzik L, Han X, et al. Nitric oxide-dependent parasympathetic signaling is due to activation of constitutive endothelial (type III) nitric oxide synthase in cardiac myocytes. J Biol Chem (1995) 270:14582–14586.[Abstract/Free Full Text]
  54. Shah A.M, Silverman H.S, Griffith E.J, et al. Cyclic GMP prevents delayed relaxation at reoxygenation following brief hypoxia in isolated cardiac myocytes. Am J Physiol (1995) 268:H2396–H2404.[Web of Science][Medline]
  55. Schluter K.D, Weber M, Schraven E, Piper H.M. NO donor SIN-1 protects against reoxygenation-induced cardiomyocyte injury by a dual action. Am J Physiol (1994) 267:H1461–H1466.[Web of Science][Medline]
  56. Balligand J.L, Ungureanu-Longrois D, Simmons W.W, et al. Cytokine-inducible nitric oxide synthase (iNOS) expression in cardiac myocytes. J Biol Chem (1994) 269:27580–27588.[Abstract/Free Full Text]
  57. Niggli E, Lederer W.J. Restoring forces in cardiac myocytes. Insight from relaxations induced by photolysis of caged ATP. Biophys J (1991) 59:1123–1135.[Web of Science][Medline]
  58. Holubarsch C, Lüdemann J, Wiessner S, et al. Shortening versus isometric contractions in isolated human failing and non-failing left ventricular myocardium: dependency of external work and force on muscle length, heart rate and inotropic stimulation. Cardiovasc Res (1998) 37:46–57.[Abstract/Free Full Text]
  59. Cheng H, Lederer W.J, Cannell M.B. Calcium sparks: elementary events underlying excitation–contraction coupling in heart muscle. Science (1993) 262:740–744.[Abstract/Free Full Text]
  60. Lipp P, Niggli E. Submicroscopic calcium signals as fundamental events of excitation–contraction coupling in guinea-pig cardiac myocytes. J Physiol (1996) 492:31–38.[Abstract/Free Full Text]
  61. Cheng H, Lederer M.R, Lederer W.J, et al. Calcium sparks and [Ca2+](i) waves in cardiac myocytes. Am J Physiol (1996) 270:C148–C159.[Web of Science][Medline]
  62. Bers DM. Excitation–contraction coupling and cardiac contractile force. Dev Cardiovasc Med 1991;122:1–258.
  63. Stern M.D. Theory of excitation–contraction coupling in cardiac muscle. Biophys J (1992) 63:497–517.[Web of Science][Medline]
  64. Barry W.H, Bridge J.H.B. Intracellular calcium homeostasis in cardiac myocytes. Circulation (1993) 87:1806–1815.[Abstract/Free Full Text]
  65. Brutsaert D.L, Sys S.U. Relaxation and diastole of the heart. Physiol Rev (1989) 69:1228–1315.[Abstract/Free Full Text]
  66. Krueger J.W, Forletti D, Wittenburg B.A. Uniform sarcomere shortening behaviour in isolated cardiac cells. J Gen Physiol (1980) 76:587–607.[Abstract/Free Full Text]
  67. Labeit S, Kolmerer B, Linke W.A. The giant protein titin. Emerging roles in physiology and pathophysiology. Circ Res (1997) 80:290–294.[Abstract/Free Full Text]
  68. Granzier H.L, Irving T.C. Passive tension in cardiac muscle: contribution of collagen, titin, microtubules, and intermediate filaments. Biophys J (1995) 68:1027–1044.[Web of Science][Medline]
  69. Helmes M, Trombitas K, Granzier H. Titin develops restoring force in rat cardiac myocytes. Circ Res (1996) 79:619–626.[Abstract/Free Full Text]
  70. Hori M, Sato H, Kitakaze M, et al. β-Adrenergic stimulation disassembles microtubules in neonatal rat cultured cardiomyocytes through intracellular Ca2+ overload. Circ Res (1994) 75:324–334.[Abstract/Free Full Text]
  71. Tsutsui H, Ishihara K, Cooper G. Cytoskeletal role in the contractile dysfunction of hypertrophied myocardium. Science (1993) 260:682–687.[Abstract/Free Full Text]
  72. Tagawa H, Wang N, Narishige T, et al. Cytoskeletal mechanics in pressure-overload hypertrophy. Circ Res (1997) 80:281–289.[Abstract/Free Full Text]
  73. Fabiato A, Fabiato F. Dependence of calcium release, tension generation and restoring forces on sarcomere length in skinned cardiac cells. Eur J Cardiol (1976) 4(Suppl.):13–27.[Medline]
  74. Krueger J. Rapid relengthening in isolated cardiac cells and the origin of diastolic recoil. In: Hori M, Suga H, Baan J, Yellin EL, editors. Cardiac mechanics and function in the normal and diseased heart, Tokyo: Springer–Verlag, 1989:23–34.
  75. Sys S.U, de Keulenaer G.W, Brutsaert D.L. Physiopharmacological evaluation of myocardial performance. Cardiovasc Res (1998) 39:136–147.[Free Full Text]
  76. Méry P.F, Pavoine C, Belhassen L, et al. Nitric oxide regulates cardiac Ca2+ current. J Biol Chem (1993) 268:26286–26295.[Abstract/Free Full Text]
  77. Wahler G.M, Dollinger S. Nitric oxide donor SIN-1 inhibits mammalian cardiac calcium current through cGMP-dependent protein kinase. Am J Physiol (1995) 268:C45–C54.[Web of Science][Medline]
  78. Pfitzer G, Ruegg J.C, Flockerzi V, Hofmann F. cGMP-dependent protein kinase decreases calcium sensitivity of skinned cardiac fibers. FEBS Lett (1982) 149:171–175.[CrossRef][Web of Science][Medline]
  79. Oddis C.V, Finkel M.S. Cytokine-stimulated nitric oxide production inhibits mitochondrial activity in cardiac myocytes. Biochem Biophys Res Commun (1995) 213:1002–1009.[CrossRef][Web of Science][Medline]
  80. Zhang X.P, Xie Y.W, Nasjletti A, et al. ACE inhibitors promote nitric oxide accumulation to modulate myocardial oxygen consumption. Circulation (1997) 95:176–182.[Abstract/Free Full Text]
  81. Seki T, Hagiwara H, Naruse K, et al. In situ identification of messenger RNA of endothelial type nitric oxide synthase in rat cardiac myocytes. Biochem Biophys Res Commun (1996) 218:601–605.[CrossRef][Web of Science][Medline]
  82. Luss H, Watkins S.C, Freeswick P.D, et al. Characterization of inducible nitric oxide synthase expression in endotoxaemic rat cardiac myocytes in vivo and following cytokine exposure in vitro. J Mol Cell Cardiol (1995) 27:2015–2029.[CrossRef][Web of Science][Medline]
  83. Dzau V.J, Gibbons G.H, Kobilka B.K, Lawn R.M, Pratt R.E. Genetic models of human vascular disease. Circulation (1995) 91:521–531.[Abstract/Free Full Text]
  84. Majzoub J.A, Muglia L.J. Knockout mice. New Engl J Med (1996) 334:904–907.[Free Full Text]
  85. Keating M.T, Sanguinetti M.C. Molecular genetic insights into cardiovascular disease. Science (1996) 272:681–685.[Abstract]

Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?



This Article
Right arrow Extract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow E-letters: Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when E-letters are posted
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Shah, A. M
Right arrow Articles by Lakatta, E. G
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Shah, A. M
Right arrow Articles by Lakatta, E. G
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?